Research On Oscillation And Stability Of GaN-Based Circuits

Gallium nitride(GaN)devices have become the focus of application based on high switching speed,low on-resistance and high current density.However,the switching speed of GaN devices is extremely fast in applications,and when the loop layout design requirements are met,the damping of high-frequency loops is small,which can cause the circuit to be susceptible to false turn-on oscillations and bring about stability problems of GaN-based circuits,such as divergent oscillations,especially in bridge circuits.Therefore,this dissertation will research the problem of oscillation and circuit stability in bridge circuits from two aspects of circuit and stability.Firstly,based on the double-pulse equivalent circuit,the oscillation mechanism of false turn-on of inactive devices of two different GaN devices in a bridge structure is analyzed.It is concluded that the Non-Kelvin package GaN device is composed of the charge-discharge current of the gate drain capacitor and the induced voltage on the common inductor,which is the main oscillation factor.And Kelvin package GaN device is mainly composed of gate drain capacitor charge-discharge current constitutes the main factor of oscillation.The correctness of the theoretical analysis is verified by LTSpice simulation.Secondly,by comparing the stability criteria of two oscillators,the theory of negative resistance oscillators is used as the stability criterion for GaN-based circuits.A small signal model of turn-on and turn-off oscillation was established for two different GaN-based circuits with different packages,and an analog negative conductance model was constructed to determine the stability of the GaN-based circuit.It is concluded that the stability of the GaN-based circuit is related to the transconductance coefficient gm1 of the inactive devices,and the larger the gm1 is,the more likely the divergent oscillation occurs in the circuit.Non-Kelvin package GaN devices are prone to divergent oscillations during turn-on,whereas Kelvin GaN package device circuits are not prone to stability problems.The correctness of the theoretical analysis was verified by double pulse test platform.Finally,the suppression measures for improving the stability of GaN-based circuits are analyzed from the point of view of active and passive suppression.For active suppression measures,a GaN half-bridge module with a GS66508D is designed to reduce the upper parasitic inductance to 1/10 or more,and the steps and methods for determining the stability of the GaN-based circuit are given.And the passive suppression measures with additional dampers were simulated and analyzed.